In trace analysis, heating equipment, usually referred to as tubular graphite furnaces, are usually used as electrothermal atomizers. In recent years, sample carriers, which are referred to as platforms and can be introduced into the tubular graphite furnaces, have increasingly been used. To achieve as isothermal an atomization as possible, which is important especially for real sample analyses, it is necessary to provide means for preheating the gas atmosphere in the interior of the tubular graphite furnace before the vaporization and atomization of the material to be analyzed commences.
Among the variously proposed atomization apparatuses which are said to ensure isothermal conditions, such as the T cuvette, (DE OS No. 2,713,637), double-wall furnace (U.S. Pat. No. 4,407,582), graphite probe technique (DE OS No. 3,044,627, DE-OS No. 3,217,417) and the platform technique, the latter has gained acceptance on the basis of its simplicity and the problem-free metering of sample solutions.
It is disclosed in DE OS No. 2,924,123 that rectangular platforms of solid pyrographite, which are fixed in a groove that runs axially symmetrically to the tube axis, may be used in standard graphite tubes.
Furthermore, it is disclosed in DE Utility Patent No. 7,825,590 that a sample carrier may be used having an outer surface which lies against the inner wall of the cuvette.
To limit the contact between the platform and the graphite tube as much as possible, DD WP 227,523 discloses that the platform be provided with small supporting feet. It is a disadvantage of these proposed solutions that, due to the construction, the heating curent flows through the sample carriers which or the sample carriers are in direct contact with the tubular graphite furnace, so that, aside from the heat radiating from the wall of the tube, the heated platform itself contributes to a considerable extent to the vaporization and atomization. The desired delayed atomization can thus be realized only to an unsatisfactory extent.
A variation of the platform measurements is also known in which the platform is pushed from the front through a slit into the cuvette. The slit, however, is precisely in the hot zone of the furnace, so that here also the thermal conduction does not lead to an optimum delay in the platform heating in relation to the tube wall. Moreover, for reasons of space, the atomizer configuration is restricted to a rectangular cuvette geometry which is extremely expensive to manufacture.